Gyroscopes (sometimes also referred to as “gyros”) are devices that are able to sense angular velocity. Gyroscopes can be mechanical or optical, and vary in precision, performance cost and size. The applications include, but are not limited to, military, aircraft navigation, robotics, autonomous vehicles, virtual reality, augmented reality, gaming etc. Optical gyroscopes typically have the highest performance and are based on interferometric measurements and the Sagnac effect (a phenomenon encountered in interferometry that is elicited by rotation). Since optical gyroscopes do not have any moving parts, they have advantages over mechanical gyroscopes as they can withstand effects of shock, vibration and temperature variation better than the mechanical gyroscopes with moving parts. The most common optical gyroscope is the fiber optical gyroscope (FOG). Construction of a FOG typically involves a long loop (or a coil comprising several loops) of polarization-maintaining (PM) fiber. Laser light is launched into both ends of the PM fiber traveling in different directions. If the fiber coil is moving, the optical beams experience different optical path lengths with respect to each other. By setting up an interferometric system, one can measure the small path length difference that is proportional to the area of the enclosed loop and the angular velocity of the rotating coil.
Phase signal of an optical gyro is proportional to the Sagnac effect times the angular rotation velocity, as shown in the following equation:Δϕ=(8πNA/λc)Ωwhere, N=number of turns in the gyro,
A=area enclosed
Ω=angular rotation velocity
Δϕ=optical phase difference signal
λ=wavelength of light
c=speed of light
These FOG's can have very high precision, but at the same time, they are of large dimension, are very expensive, and are hard to assemble due to the devices being built based on discrete optical components that need to be aligned precisely. Often, manual alignment is involved, which is hard to scale up for volume production.